As is well known in the art, Stirling Engines convert a temperature difference directly into movement. Such movement, in turn, may be converted into mechanical or electrical energy. The Stirling Engine cycle comprises the repeated heating and cooling of a sealed amount of working gas. When the gas in the sealed chamber is heated, the pressure increases and acts on a piston thereby generating a power stroke. When the gas in the sealed chamber is cooled, the pressure decreases and is acted upon by the piston thereby generating a return stroke.
Stirling Engines, however, require an external heat source to operate. The heat source may be the result of combustion and may also be solar or nuclear. In practicality, the rate of heat transfer to the working fluid within the Stirling Engine is one primary mechanism for increasing the power output of the Stirling Engine. One skilled in the art, however, will recognize that power output may be increased through a more efficient cooling process as well.
U.S. Pat. No. 5,590,526 to Cho describes a conventional prior art burner for a Stirling Engine. Generally, a combustion chamber provides an air-fuel mixture for the burner by mixing air and fuel supplied from air inlet passageways and a fuel injection nozzle, respectively. An igniter produces a flame by igniting the air-fuel mixture formed within the combustion chamber. A heater tube absorbs high temperature heat generated by the combustion of the air-fuel mixture and transfers the heat to the Stirling Engine working fluid. Exhaust gas passageways discharge an exhaust gas.
A more efficient heat source is described in U.S. Pat. No. 5,918,463 to Penswick, et al. (hereinafter referred to as “Penswick”) in order to overcome the problem of delivering heat at non-uniform temperatures. As described by Penswick, Stirling engines require the delivery of concentrated thermal energy at uniform temperature to the engine working fluid. (See Penswick Column 1, lines 39-40). In the approach disclosed by Penswick, a burner assembly transfers heat to a Stirling Engine heater head primarily by radiation and secondarily by convection. (See Penswick Column 1, lines 58-61). Penswick discloses the device with respect to an external combustion engine, a Stirling Engine, and a Stirling Engine power generator. (See Penswick Column 2, lines 36-66).
With respect to the external combustion engine, the Penswick burner assembly includes a housing having a cavity sized to receive a heater head and a matrix burner element carried by the housing and configured to transfer heat to the heater head. (See Penswick Column 2, lines 38-41). With respect to the Stirling Engine, the Penswick burner assembly includes a housing having a cavity sized to receive a heater head and a matrix burner element configured to encircle the heater head in spaced apart relation. (See Penswick Column 2, lines 48-51). Lastly, with respect to the Stirling Engine power generator, the Penswick burner assembly includes a housing having a cavity sized to receive the heater head and a matrix burner element configured to encircle the heater head in spaced apart relation. (See Penswick Column 2, lines 63-66).
The Penswick burner housing supports a fiber matrix burner element in radially spaced apart, but close proximity to, a radially outer surface of the Stirling Engine heater head. (See Penswick Column 4, lines 19-21). Penswick further discloses that combustion may occur in radiant or blue flame. In the radiant mode, combustion occurs inside matrix burner element which, in turn, releases a major portion of the energy as thermal radiation. In the blue flame mode, blue flames hover above the surface and release the major part of the energy in a convective manner. (See Penswick Column 4, lines 42-54). Hence, operation of the Penswick burner requires space between the combusting matrix element and the heater head in order to operate in any of the modes disclosed by Penswick.
Moreover, Penswick describes a heat chamber that is formed within the burner housing between the inner surface of the matrix burner element and the outer surface of the Stirling Engine heater head. Heat transfer occurs within the heat chamber primarily through radiation from the matrix burner element to the Stirling Engine heater head, and secondarily via the passing of hot exhaust gases over the Stirling Engine heater head. (See Penswick Column 6, lines 1-7, and FIG. 5). According to Penswick, heat being delivered through the heat chamber and over the Stirling Engine heater head is conserved as a result of insulation. (See Penswick Column 7, lines 17-20). However, a problem still exists in the art with respect to enhancing the efficiency of the operation of a Stirling Engine.
As recognized by one skilled in the art, the uniform burning of a matrix burner element remains a problem. In U.S. Pat. No. 6,183,241 to Bohn, et al. (hereinafter referred to as “Bohn”), computer simulation was employed to develop an inward-burning, radial matrix gas burner to attempt to solve the difficulty of obtaining uniform flow and uniform distribution in a burner matrix. (See Bohn, Abstract and Column 1, lines 54-56). According to Bohn, metal matrix burners have received much attention because of their ability to burn fossil fuels with very low emissions of nitrogen oxides. (See Bohn, Column 1, lines 37-39). With respect to the transfer of heat to the Stirling Engine heater head, Bohn also teaches that a significant fraction of the heat of combustion is released as infrared radiation from the matrix. (See Bohn, Column 1, lines 42-44).
Bohn's solution provides a high-temperature uniform heat via a cylinder-shaped radial burner, a curved plenum, porous mesh, divider vanes, and multiple inlet ports. Extended upstream fuel/air mixing point provide for uniform distribution of a preheated fuel/air mixture. (See Bohn, Column 4, lines 56-61). Bohn teaches the use of a space formed between a heat pipe and the burner matrix and the use of a mesh screen therebetween to promote uniform radiant heat transfer. Unfortunately, the solution offered by Bohn still is too complex and inefficient for desired uses.
Yet another method for transferring heat to the heater head of a Stirling Engine is disclosed in U.S. Pat. No. 6,877,315 to Clark, et al. (hereinafter referred to as “Clark”). According to Clark, the Stirling Engine heater head is generally arranged vertically with a burner surrounding it to supply heat so that hot exhaust gases from the burner can escape upwards. The device disclosed by Clark enhances the transfer of heat to the Stirling Engine heater head to increase its efficiency by employing fins to increase the heater head surface area. (See Clark, Column 1, lines 19-33). Clark teaches that a problem still exists in the art with respect to the effective and efficient transfer of heat to a Stirling Engine heater head as late as 2003.
In the device disclosed by Clark, an annular burner surrounds the heat transfer head and provides the heat source. The heat transfer head is provided with a plurality of fins to promote and enhance heat transfer. (See Clark, FIG. 1 and Column 2, lines 34-45). Radiant heat is transferred to the heater head and also to other substantially parallel fins to further enhance the heat transfer. (See Clark, Column 1, lines 63-65). As with the other prior art cited, the relative spaced-apart relationship that allows heat to be transferred radiantly is important. Clark teaches that the source of radiant heat is arranged opposite to the plurality of fins such that radiant heat is directed into the spaces between adjacent fins. (See Clark, Column 3, lines 4-6).
Another problem with burner devices for a Stirling Engine is described in U.S. Pat. No. 6,513,326 to Maceda, et al. (hereinafter referred to as “Maceda”). Maceda discloses a conventional burner device in which air and fuel are injected into the burner and then ignited to cause heat to be generated. The working gas is carried within a plurality of heater tubes that are positioned proximate to the burner device so that heat is transferred from the burner device to the working gas flowing within the heater tubes. (See Maceda, Column 1, lines 39-46). As known to one skilled in the art, the heater tubes are positioned proximate to the burner device such that heat can be radiantly transferred from the burner device to the tubes.
According to Maceda, heat is not uniformly distributed to the working gas within the heater tubes because a single burner device is used to generate and effectuate the heat transfer. (See Maceda, Column 1, lines 55-59). As a solution to the problem of uniform heat distribution, Maceda teaches the use of a heat exchange manifold employing multiple platelets that are stacked and joined together. (See Maceda, Column 2, lines 22-24). Instead of having one large burner device with one combustion chamber and a multiple of heater tubes per piston cylinder, the Maceda manifold provides a substantially greater number of individual combustion chambers. (See Maceda, Column 2, lines 51-57). Unfortunately, the solution offered by Bohn still is too complex and inefficient for desired uses.
Based on the foregoing, what is need is a simple, efficient and effective method and apparatus for generating and transferring heat to the heater head of a Stirling Engine. A method for generating and transferring heat to the heater head of a Stirling Engine is currently being prosecuted under Applicants' U.S. patent application Ser. No. 11/364,402. An apparatus for generating and transferring heat to the heater head of a Stirling Engine is described and claimed hereinbelow.